Congenital birth defects are one of the lading causes of neonatal morbidity and mortality. Human heterotaxy syndromes, such as Kartagener syndrome, often have associated lethal cardiac defects and defects in ciliary structure and function. Understanding the origins of these defects requires an elucidation of the mechanisms underlying the normal development of the embryo. Winged helix transcription factors play important roles during development by regulating cellular differentiation and cell - specific gene expression. Hepatocyte nuclear factor/forkhead homologue (HFH) - 4 is a member of the winged helix family expressed during development in a variety of epithelial tissues. Mice homozygous for disruption of the hfh-4 gene have congenital abnormalities of the left-right axis asymmetry and lack cilia. HFH-4 is thus essential for determination of left-right axis asymmetry and ciliated cell differentiation during development. In the proposed studies, we will begin to elucidate the mechanisms of left-right asymmetry determination and ciliated epithelial cell differentiation by HFH-4. To begin to understand the genetic pathways involved in left-right asymmetry the early embryonic pattern of HFH-4 expression will be determined and the expression patterns of other ~left-right~ genes will be studied in hfh-4 mice. The structure of ciliated epithelium in hfh-4 mice will be studied by electron microscopy, as well as determination of the expression of genes associated with ciliated cell differentiation.. Differential display will be used to identify potential target genes for HFH-4. The human HFH-4 gene will be isolated and characterized and single chain conformation polymorphism analysis used to identify mutations in the human HFH-4 gene. Elucidating the cellular and molecular mechanisms regulating the determination of left-right asymmetry has great significance for vertebrate development and the pathology of human congenital malformations. Insights into the differentiation of ciliated cells have important implications for understanding the respiratory function and pathology and for reproductive function and infertility.